In the heat processing of products and materials it is often required to maintain in a furnace chamber a predetermined gas environment which may be of critical composition, such as CO.sub.2 or CO in equilibrium, or which may be dangerous. Leakage of gas from the furnace chamber can affect the intended furnace environment and can release dangerous gas outside of the furnace with possibly serious consequences. Leakage of air into the furnace can also have deleterious and possibly hazardous effects. Gas leakage from the furnace as well as air leakage into the furnace usually occur around the door by which the furnace is loaded and unloaded. The requirements for an efficient furnace door seal have been incompatible with the requirements for easy access to the furnace for loading and unloading purposes.